The present invention relates to a gas turbine segmental ring made in such a structure that a cooling air leakage from connecting portions of segment structures is reduced as well as a thermal deformation in each of the segment structures and a restraining force caused by the thermal deformation are reduced.
FIG. 4 is a cross sectional view generally showing a front stage gas path portion of a gas turbine. In FIG. 4, immediately downstream of a fitting flange 31 of a combustor 30 in a flow direction of combustion gas 50, a first stage stationary blade (1c) 32 has both its ends fixed to an outer shroud 33 and inner shroud 34 and a plurality of the first stage stationary blades 32 are arranged in a turbine circumferential direction being fixed to an inner side of a turbine casing on a stationary side of the gas turbine. Downstream of the first stage stationary blade 32, a plurality of first stage moving blades (1s) 35 are arranged in the turbine circumferential direction being fixed to a platform 36. The platform 36 is fitted around a rotor disc and thus the moving blade 35 rotates together with a rotor (not shown). Along the turbine circumferential direction close to a tip of the moving blade 35, a segmental ring 42 of an annular shape formed of a plurality of segment structures is arranged being fixed to the turbine casing side.
Downstream of the first stage moving blade 35, a second stage stationary blade (2c) 37 has both its ends fixed to an outer shroud 38 and inner shroud 39 and likewise a plurality of the second stage stationary blades 37 are arranged in the turbine circumferential direction being fixed to the stationary side. Also, downstream thereof, a plurality of second stage moving blades (2s) 40 are arranged in the turbine circumferential direction being fixed to a rotor disc (not shown) via a platform 41. Along the turbine circumferential direction close to the tip of the moving blade 40, likewise a segmental ring 43 formed of a plurality of segment structures is arranged. The gas turbine having such a blade arrangement is usually constructed of four blade stages and the combustion gas 50 of a high temperature generated at the combustor 30 flows in the first stage stationary blade (1c) 32. While the combustion gas 50 passes through the respective blades of the second to the fourth stages, it expands to rotate the moving blades 35, 40, etc. and thus to rotate the rotor and is then discharged.
FIG. 5 is a cross sectional view showing a detail of the segmental ring 42 that is arranged close to the tip of the first stage moving blade 35, as described above. In FIG. 5, numeral 60 designates an impingement plate, that is fitted to a heat insulating ring 65 on the turbine casing side and comprises a plurality of through holes as cooling holes 61. The segmental ring 42 also is fitted to the heat insulating ring. 65 and comprises a plurality of cooling passages 64 bored in the respective segment structures along a turbine axial direction or along a direction of main flow gas 80. Each of the cooling passages 64 has at one end an opening 63 that opens in an upper surface of the segmental ring 42 on the upstream side and has at the other end an opening that opens in a circumferential side end surface of the segmental ring 42 on the downstream side, as shown in FIG. 5.
In the construction described above, cooling air 70 bled from a compressor or supplied from an outside cooling air supply source flows through the cooling holes 61 of the impingement plate 60 to enter a cavity 62 below the impingement plate 60 and to impinge on the segmental ring 42 for effecting a forced cooling or impingement cooling of the segmental ring 42. Then, the cooling air 70 in the cavity 62 flows into the cooling passages 64 from the openings 63 for cooling an interior of the segmental ring 42 and is discharged into the main flow gas 80 from the openings of the rear end of the segmental ring 42.
FIG. 6 is a partial perspective view of the segmental ring 42 described above. As shown there, the segmental ring 42 is formed in the annular shape of the plurality of segment structures arranged and connected to one another in the turbine circumferential direction. The impingement plate 60 is arranged above, or on the outer side of, the segmental ring 42 and the cavity 62 is formed between the impingement plate 60 and a recessed portion of the upper side of the segmental ring 42. Thus, as mentioned above, the cooling air 70 entering the cavity 62 through the cooling holes 61 impinges on an upper wall surface of the segmental ring 42 to forcibly cool the segmental ring 42 and then flows through the cooling passages 64 to cool the interior of the segmental ring 42 and is discharged into the main flow gas 80.
In the gas turbine segmental ring, in order to prevent a reverse flow of the main flow gas 80, pressure of the cooling air 70 in the cavity 62 is made higher relative to that of the main flow gas 80. Hence, in addition to the amount of the cooling air flown through the segmental ring 42 and effectively used for the cooling thereof, there is some amount of the air leaking from connecting portions of the segment structures of the segmental ring 42. Thus, as the number of the segment structures becomes larger, the number of the connecting portions thereof becomes larger and the amount of the leaking air becomes also larger, which results in the reduction of the cooling efficiency. Moreover, as the surface of the segmental ring 42 is directly exposed to the high temperature main flow gas 80, unusual force due to thermal deformation of the segment structures may arise so that a roundness of the segmental ring 42 may be hardly maintained, which results in causing an increase of the air amount leaking from the connecting portions and in giving an unfavorable influence on the clearance between the tip of the moving blade 35 and the segmental ring 42.
In view of the problems in the prior art, it is an object of the present invention to provide a gas turbine segmental ring made in such a structure that the number of segment structures forming the segmental ring is lessened so as to reduce a cooling air leakage amount and each of the segment structures is formed so as to reduce a thermal deformation thereof as well as to absorb a distortion caused by the thermal deformation.
In order to achieve the mentioned object, the present invention provides the means of the following inventions (1) and (2):
(1) A gas turbine segmental ring formed in an annular shape of a plurality of segment structures connected to one another in a turbine circumferential direction and arranged to be fitted to an inner circumferential surface of a turbine casing with a predetermined clearance being maintained between itself and a tip of a moving blade, each of the segment structures having at its turbine axial directional front and rear end portions flanges extending in the turbine circumferential direction to be fitted to the turbine casing, characterized in that each of the segment structures is constructed such that the flanges have their flange portions cut in so that a plurality of slits may be formed along the turbine axial direction and a plurality of ribs arranged to form a lattice shape are provided to project from an upper surface existing between the flanges of the segment structure.
(2) A gas turbine segmental ring as mentioned in the invention (1) above, characterized in being formed in the annular shape of 15 pieces of the segment structures.
In the invention (1) above, as the plurality of slits are formed in the flanges to be fitted to the turbine casing, even if the thermal deformation may arise, it can be absorbed by the deformation of these slits. Also, as the waffle pattern of the ribs is formed on the upper bottom surface of the segment structure to increase the rigidity, the thermal deformation of the segment structures can be suppressed to the minimum and the roundness of the segmental ring can be secured.
In the invention (2) above, the annular shape of the segmental ring is formed of the 15 pieces of the segment structures, which is a half of 30 pieces of the segment structures of the prior art case. Thereby, the connecting portions of the segment structures are also reduced to the half of the prior art case, the cooling air amount leaking from the connecting portions can be remarkably reduced and the cooling efficiency can be greatly enhanced.